More than half of the Americans who suffer from depression now seek treatment, up from one-third 10 years ago, a new survey says. Yet nearly 60 percent of the people in treatment do not receive adequate care, the researchers found.

More than 16 percent of Americans — as many as 35 million people — suffer from depression severe enough to warrant treatment at some time in their lives, according to the National Comorbidity Study, sponsored by the National Institutes of Health and published today in a special issue on depression of The Journal of the American Medical Association. In any given one-year period, 13 million to 14 million people, about 6.6 percent of the nation, experience the illness.

The numbers are similar to those found in the first survey 10 years ago. At that time, the lifetime prevalence of depression was measured at nearly 15 percent and the one-year figure at 8.6 percent.

Depression costs employers $44 billion a year in lost productive time, according to a second survey reported in the same issue of the journal. That figure is $31 billion more than the amount lost because of illnesses in people who do not have depression. The participants were asked about their wages and lost hours.

Most of the lost time occurs while people are at work, said the lead researcher, Dr. Walter F. Stewart, an epidemiologist now at Geisinger Health Care Systems in Danville, Pa.

"People are making it to work," Dr. Stewart said. "They're just not engaged in work. They're getting to the door, but then closing it and just not functioning. People have called this `presenteeism,' and it is often invisible to employers."

An important reason that people with depression fail to receive proper care, said Dr. Ronald Kessler, the leader of the N.I.H. survey who is a professor of health care policy at Harvard, is that many people seek help from family doctors, who often do not treat depression aggressively.

"Family doctors are apparently not yet up to speed enough to give good quality care," Dr. Kessler said.

In the survey, which included interviews with more than 9,000 people, treatment was considered adequate if it consisted of at least eight half-hour sessions of counseling with a mental health professional or treatment with antidepressant drugs for at least 30 days, combined with four visits to a doctor.

In some cases, the researchers found, patients with depression were given just 5 milligrams of antidepressant, one-fourth the standard dose.

Dr. Kessler said family practitioners could easily learn to improve their treatments.

"The bigger nut to crack," he said, "has been getting people to come into treatment. And in that area, we've made significant progress."

The director of the National Institute of Mental Health, Dr. Thomas R. Insel, said depressed people often discontinued their treatments.

"Depression," Dr. Insel said, "brings a tremendous sense of hopelessness. When you're in the middle of it, you can't remember that things were ever any better."

The illness displays sadness, hopelessness and difficulty concentrating.

The survey found that women continued to have a higher risk for depression than men, though the gap is narrowing. Women who have had at least one episode of depression outnumbered men 1.7 to 1. Forty to 50 years ago, the ratio was three to one, Dr. Kessler said, and 10 years ago, it was two to one.

Black people are 40 percent less likely to experience depression than Hispanic or white people, the survey said. On the other hand, blacks who develop the disorder are 30 percent more likely to suffer lasting or recurring depression.

People living in poverty are nearly four times as likely to suffer chronic depression as affluent people, the survey reported.

Younger people are also at risk. Among those experiencing depression in a one-year period, three times as many people were from 18 to 29 as were 60 and older.

That depression strikes so early in life is an important reason why it is such a significant health problem worldwide, Dr. Kessler said.

"Hypertension and arthritis start at age 55," he said. "Depression starts at 15 or 25. So the number of years of suffering in a person's life is much higher."

A third paper in the journal focuses on the high rate of doctors' suicides. Although no recent studies of suicide among doctors in the United States have been conducted, doctors in international studies have been found to be significantly more likely to commit suicide than other people of their sex and age.

Although in the general population men are more likely than women to commit suicide, among doctors, women and men are equally at risk.

Because so many American doctors have quit smoking, their health is generally better than that of other people their age.

"Doctors have lower heart disease rates and lower cancer rates," said Dr. Daniel E. Ford, of the Johns Hopkins University Medical Center, an author of the study. "The suicide rate really sticks out there as the one rate that's different."

The numbers suggest that doctors are not as adept as they should be at recognizing and treating depression and mood disorders, said Dr. J. John Mann of the Columbia University Medical Center, president of the American Foundation for Suicide Prevention and another author of the study. "Physicians need to take better care of themselves and translate that into the way they care for their patients."

Dr. Insel, an author of an editorial in the journal on depression, noted that doctors were better at treating the disorder than at understanding it.

"We don't understand the pathophysiology," he said. "And there is no biomarker. We don't have a P.S.A. test for depression."

That was a reference to the blood test used to help diagnose prostate cancer.

A better understanding is crucial, Dr. Insel said, because depression affects the entire body.

"It's not just people feeling lousy," he said. "Depression affects the cardiovascular system, the endocrine system, even bone growth leading to osteoporosis."

Depression develops in one in four people who have had heart attacks. When it strikes, the risk of dying is three and a half times greater than if the victims were not depressed, studies show, making it as great a risk factor as smoking.

A study of nearly 2,500 people, also in the journal, looked at whether treating for depression after a heart attack would improve survival. Treatment, with antidepressants or counseling, was found to reduce depression and improve social functioning, but it did not influence survival.

Dr. Susan M. Czajkowski, a research psychologist at the National Heart, Lung and Blood Institute who is an author of the study, said future studies might find that stronger treatments or therapy at a different time, perhaps before the first heart attack, might make a difference in survival.

"We need another trial," Dr. Insel said. "We need a really serious large-scale study to see whether you're going to save lives in people who've had a heart attack by treating their depression."